Recloser With Integrated Grounding - Alternative To Direct Transfer Trip For der

Utility generation interconnection standards may mandate that all distributed energy resources (DER) connected downstream of a fault interruption device on a feeder come offline following the trip operation of the feeder breaker or recloser within hundreds of milliseconds following operation. This is generally for safety even if IEEE 1547-2018 mandates a two second DER disconnection time following islanding events. This is typically achieved by requiring all large DER sites to install direct transfer trip (DTT); for reliability, optical fiber communication with a continuous carrier allows the interruption relay(s) to send a direct transfer trip (DTT) signal to the point of interconnection (POI) device or the generator breaker. The deployment of fiber networks is an expensive proposition and as the amount of DER on the feeder increases, the fiber utilization increases in complexity. The associated costs may prove a detriment to DER deployments. These DTT schemes also involve challenges when routine switching changes the upstream protective devices associated with the DER facility. In this paper, a highspeed grounding scheme is proposed as an alternative to the communication based direct transfer trip (DTT) scheme typically employed to bring large distribution connected distributed energy resources offline when there is a fault on the feeder. The highspeed grounding scheme consists of two switching devices – one a traditional protective device connected in series with the feeder and the second, a fast-switching device (grounding device) that is connected to the load side (down-stream side) of the protective device. Activating the fast-switching device is executed once the protective device opens to interrupt a fault. The fault event closes the fast-switching device and grounds the load section of the feeder. Such an act of grounding the isolated down-line feeder initiates the disconnection of DER even in the case of high impedance faults which the DER device(s) may fail to detect at its terminals. The scheme is designed such that it can be retrofitted to any currently installed feeder breaker or midline recloser on a 4-wire multi-grounded distribution system. This grounding will be seen by every down-stream DER relay connected to the phase wires; separate communication to each site is not needed. The scheme was developed in conjunction with a US-based utility with a focus on their distribution system. Logic was developed specifically for their standard recloser package to allow for an addition of a grounding device to their existing protection devices without extensively modifying current protection practices. Hardware in the loop testing was performed to evaluate the performance of the scheme under various system conditions including automated looped scheme operations. The testing included the actual switching devices in addition to the control relays so timing could be observed. DER was also included in some of the tests so that current and voltage waveforms from the grounded DER could be recorded.